Servomechanism including a polyphase alternating current synchronous motor

ABSTRACT

A servomechanism including a polyphase alternating current synchronous motor and a variable frequency, variable magnitude voltage generating means, said generating means comprising transducing apparatus responsive to the position of the rotor of said motor as well as to a desired speed signal and an actual speed signal to generate signals signifying those components of the voltages to be applied to the stator phase windings of said motor to balance, one, the counter electromotive fore which would be produced across each phase winding at no load at the speed at which the rotor is then rotating and the resistance voltage drop produced across each phase winding by the current then flowing therein, and, two, the leakage and the synchronous reactance voltage drop produced across each phase winding by the current then flowing therein and at the speed at which the rotor is then rotating. These transducing apparatus signals for each phase, after being summed vectorially, caused signal translating apparatus of the voltage generating means to apply voltages to their respective stator phase windings to operate said motor according to said desired speed signal.

United States Patent 1 Krauer [54] SERVOMECHANISM INCLUDING A POLYPHASEALTERNATING CURRENT SYNCHRONOUS MOTOR [75] Inventor; Otto AlbertKrauer,Tuckahoe,N.Y.

Manteuffel ..3l8/175 Primary Examiner-T. E. Lynch Attorney-Joseph L.Sharon and Robert T. Mayer 1 1 June 5, 1973 ABSTRACT generating meanscomprising transducing apparatus responsive to the position of the rotorof said motor as well as to a desired speed signal and an actual speedsignal to generate signals signifying those components of thevoltages'to be appli d to the stator phase windings of said motor to baance, one, the counter electromotive fore which would be produced acrosseach phase winding at no load at the speed at which the rotor is thenrotating and the resistance voltage drop produced across each phasewinding by the current then flowing therein, and, two, the leakage andthe synchronous reactance voltage drop produced across each phasewinding by the current then flowing therein and at the speed at whichthe rotor is then rotating. These transducing apparatus signals for eachphase, after being summed vectorially, caused signal translatingapparatus of the voltage generating means to apply voltages to theirrespective stator phase windings to operate said motor according to saiddesired speed signal.

12 Claims, 1 Drawing Figure E Q9 VDSY 78m,

SERVOMECHANISM INCLUDING A POLYPHASE ALTERNATING CURRENT SYNCHRONOUSMOTOR This invention relates to servomechanisms. More particularly, itrelates to a servomechanism including a polyphase alternating currentsynchronous motor.

Where it is desired to position a movable element accurately and tomaintain it so positioned as well as to move it rapidly in apredetermined manner from one such position to another, it hasheretofore been accepted practice to employ-direct current motor controlsystems because their inherent characteristics make them ideally suitedfor such applications. Their motor speeds can be controlled accuratelyover their entire speed range from standstill to a rated running speedand they are capable of continuously producing high torque at any speedthroughout that range as well as at standstill and in starting. Thisenables such a system to start under any load within its rated capacity,to drive that load to any selected position in a predetermined mannerand to maintain it there for as long as desired.

In such systems the load, or movable element, may be coupled to thedirect current motor through gears so that the motor may operate athigher speeds than it is desired to drive the load. This permits the useof a smaller motor than would be required if such a geared coupling werenot employed. However, where fine psitioning accuracy as well asrelatively high speed operation is desired, such as in a-high speedelevator, it has been found more suitable to drive the elevator directlyby large direct current motors without a gear coupling. This eliminatesany inaccuracy which might be introduced by clearance, or backlash,between gear teeth. But because of the direct coupling between the motorand the elevator car, it has the disadvantage of substantiallyincreasing the size of the motor to obtain accurately controlled slowspeed operation.

Where extremely fine positioning accuracy is desired, such as insatellite tracking antenna systems, the diameter of the commutators ofthe direct current driv- It is still another object of this invention toprovide a servomechanism including a polyphase alternating currentsynchronous motor that is operable to start the motor under any loadwithin its rated capacity, to move the load to any selected position ina predetermined continuously controlled manner and to produce torque tomaintain the load at that position for as long as desired.

Accordingly, thereis provided a servomechanism including a polyphasealternating current motor operable in response to the continuousapplication to its rotor of any load within the capacity of theservomechanism to produce torque to maintain said rotor at zero angularvelocity at any angular position of said rotor.

ing motors must also be substantially increased to reduce thediscontinuities in position introduced by the commutator bars. Suchdiscontinuities, of course, can never be fully eliminated from directcurrent motor control systems as long as a mechanical commutator isemployed.

It is desirable to replace the direct current motors of the foregoingsystems with some type of alternating current motor. An alternatingcurrent motor requires less copper to build than a direct current motorcapable of delivering comparable torque. For this reason it is lesscostly to manufacture. Manufacturing costs are further reduced' becausean alternating current motor has no commutator. For this same reason, itrequires less service and maintenance and thus lowers these costs also.The lack of a commutator also completely eliminates the positionaldiscontinuities that are inherent in direct current motors.

It is an object of this invention to provide an improved motor controlsystem.

It is another object of this invention to provide a servomechanismincluding a polyphase alternating current motor that is operable tocontrol the out of phase currents that the motor generates therebyenhancing the torque producingcapabilities of the motor.

For convenience purposes, the invention will be described as applied inan elevator system. It is to be understood, however, that the inventionis in no way limited to such an application and is suitable for variousother applications in which direct current motor control systems arepresently employed. Also, the motor disclosed is a three phasesynchronous motor, it being understood that the invention is applicableto any polyphase alternating current synchronous motor.

Other advantages of the present invention as well as additional objectsand features thereof will be apparent to those skilled in the art fromthe following description when considered in conjunction with theappended claims and accompanying drawing, in which the sole figure is aschematic representation of a servomechanism including a polyphasealternating current synchronous motor.

Referring specifically to the drawing, there is depicted therein anelevator car 10 and its counterweight 11 supported in typical fashion byhoist ropes 12 wrapped over driving sheave 13. Sheave 13 is mounted onthe same shaft as rotor 14 of a three phase alternating currentsynchronous motor whose stator phase windings are pictoriallyrepresented by coils A, B and C. A suitable three phase synchronousmotor for an elevator installation whose duty rating is 4,000 lbs. at1,200 feet per minute and whose sheave measures 36 inches in diameterwith a moment of inertia at the motor shaft of 1,570 lbs. ft. secF/rad.includes a 14 pole permanent magnet rotor which produces a sinusoidalmagnetomotive force or flux distribution. its full load torque rating is3,900 lbs. ft. The full load rated speed of this motor is 127.5 r.p.m.with a stator frequency of 15 cycles per second and a rated statorvoltage of 200 volts with a stator current per phase of approximatelyamperes at rated load at rated speed.

Direct current tachometer generator 15 is mechanically connected in anysuitable fashion to be driven by the shaft of rotor 14 and produces asignal along lines +V and V signifying the speed of rotation of rotor14. Also connected to be driven by rotor 14 is a gear train GT. Theoutput of this gear train drives a two pole permanent magnet rotor 16 ofa Hall effect rotor position transducer to be explained hereinafter. Thegear ratio of this gear train GT is such as to drive the rotor of theposition transducer one mechanical revolution for each revolutionthrough 360 electrical degrees of rotation of rotor 14 of thesynchronous motor. Thus,

Connected to supply voltage to stator phase windings A, B and C isequipment identified as a variable frequency variable magnitude voltagegenerating means. At all frequencies within the capacity of thisequipment it applies to the individual stator phase windings voltageswhich are so related to each other in magnitude, frequency and phaseangle as to cause the stator windings to produce a sinusoidalmagnetomotive force or flux distribution. Included as part of thisequipment are pulse modulated inverter circuits A1, B1 and CI. Suitablesuch inverter circuits may take the form of the well known McMurrayinverter. Forming part of each inverter circuit but not separatelyillustrated is an individual gate control circuit. These invertercircuits are controlled by pulses applied to their gate control circuitsby pulse generators APG, BPG and CPG which operate at a pulse repetitionrate of 1,000 pulses a second.

The input signal to each pulse generator is modulated by the outputsignal of sawtooth wave generator SWG which also operates at arepetition rate of 1,000 a second. The output signal of generator SWG,as shown in the representation of the waveform illustrated belowinverter C1 in the drawing, is produced with equal halves of the waveabove and below the zero axis which is represented by the solid linemarked 0. This output signal is added to the input signal applied toeach of the pulse generators APG, BPG and CPG along lines E E,, and Erespectively, and the individual combinations of these signals passthrough level detectors (not separately shown) individual to each pulsegenerator. Each of these level detectors causes its associated pulsegenerator to produce pulses containing positive and/or negative portionsdepending upon how much of the combined signal it receives remains aboveor below the zero axis-Thus, in the representative waveform if thedotted line is now considered the zero axis such that approximatelytwo-thirds of the sawtooth wave applied to one of the pulse generatorshas been displaced below the zero axis by the input signal to the pulsegenerator, each pulse of the output signal from the pulse generator foreach such cycle of the sawtooth wave contains a portion which forapproximately one-third of the pulse is positive and a portion which forthe remainder of the pulse is negative (as illustrated below thesawtooth wave). Similarly, other proportions of positive and negativeportions from totally positive to totally negative are possibledepending upon the amount of each cycle of the sawtooth wave which isdisplaced above and below the zero axis by-the input signals to thepulse generators.

lnverter circuits A1, B1 and Cl, pulse generators APG, BPG and CPG, andsawtooth wave generator SWG comprise that part of the voltage generatingmeans hereinafter identified as signal translating apparatus. Thisapparatus, as is illustrated by the sinusoidally shaped waveformsadjacent each pulse generator and each inverter circuit, producevoltages for the phase windings A, B and C which are faithfulreproductions of the signals applied along lines 13,, E and Erespectively, in phase angle and frequency but which vary therefrom inmagnitude by a predetermined constant scale factor.

The signals applied along lines E E and E are produced by amplifiers 18through 20, respectively. Each of these is a summation amplifier whichproduces an output signal proportional to the vector sum of the inputsignals it receives from amplifiers 22 and 23 or 24 and 25 or 26 and 27,respectively. Each of amplifiers 22 through 27 is a differentialamplifier which produces an output signal referenced to ground which isdirectly proportional to the magnitude of the signal applied along itsrespective input lines E E E,,,, E E and E Amplifiers 18 through 27comprise that part of the voltage generating means hereinafter referredto as the signal summing amplifier circuitry.

Also included as part of the voltage generating means is the previouslymentioned rotor position transducer comprising the two pole permanentmagnet rotor 16 which is mounted for rotation in a cylindrical statoryoke (not shown) composed of a satisfactory magnetic material. Suitablythe permanent magnets of rotor 16 produce a sinusoidal flux distributionthroughout the stator yoke with a maximum flux of 10,000 gauss(lines/sq. cm.). Mounted in any suitable fashion at intervals around theinterior surface of the stator yoke are a plurality of Hall effectelements Al, A2, B1, B2, C1 and C2. Hall effect elements A1, B1 and C1are so mounted that the physical displacements between them correspondwith the electrical displacements between the axes of the differentphase windings of the stator poles of the motor. In the disclosedembodiment since the axes of the windings of each of the stator poles ofthe three phase motor are displaced one from the other by 120 electricaldegrees, elements A1, B1 and C1 are displaced from each other by 120mechanical degrees about the transducer stator yoke. Elements A2, B2 and30 C2 are mounted in quadrature with their respective correspondingelements.

As mentioned, rotor 14 of the motor and rotor 16 of the positiontransducer are mechanically connected through gear train GT such thateach electrical degree of revolution of rotor 14 is represented by amechanical degree of revolution of rotor 16. Furthermore this connectionis made so that whenever the seven north poles 1 v of rotor 14 arepassing in a particular direction the physical location of the sevenaxes of one of the phase windings of the stator, say phase winding A,the north pole of rotor 16 is passing in the same direction the Halleffect element A2 which is in quadrature with the element A1corresponding to phase winding A.

Current is provided for the Hall effect elements A1, B1 and Cl whosephysical locations correspond to the physical locations of the axes ofthe stator pole phase windings through a series connection from directaxis summing amplifier DAS. Similarly, current is provided for each ofthe quadrature Hall effect elements through a series connection fromquadrature axis multiplier QAM. As is well known, each Hall effectelement produces an output voltage signal along its respective outputlines E E etc. which is a function of the product of the magnitude ofthe current applied to the element from either direct axis summingamplifier DAS or quadrature axis multiplier QAM, whatever the case maybe, and the magnitude of the flux passing through the element producedby the magnetomotive force generated by rotor 16.

Direct axis summing amplifier DAS produces an output signal whosemagnitude is proportional to the sum of the magnitude of the signalalong line TD and that of the signal along line +V As will be explainedthe signal along line TD signifies the difference between a speed atwhich it is desired that rotor 14 rotate and the actual speed at whichit is rotating. It has already been stated that the signal along line +Vis produced by tachometer generator and signifies the actual speed atwhich rotor 14 is rotating. This line is designated +V to signify thatthe signal applied alongit is to be understood to be an additivefunction in the mathematical analysis of the system in contrast to thesignal along line -V,- which it is to be. understood is a subtractivefunction in such analysis.

Amplifier DAS contains two separate linear scale factors. One producesone value of current for each volt of input signal along line +V whilethe other produces a different and lesser value of current for each voltof signal along line TD. The reason for this is that in response to anyinput signal along line +V an output signal is produced .by amplifierDAS which generates applied voltages for phase windings A, B and C whichbalance the counter electromotive forces which would be produced in therespective windings at no load at the speed represented by the signalalong line +V Whereas in response to any input signal along line TD, anoutput signal is produced by amplifier DAS which generates appliedvoltage for phase windings A,

B and C which balance the resistance, or IR, voltage drops across eachwinding produced by the currents I then flowing in the windings.

Quadrature axis-multiplier QAM produces an output signal whose magnitudeis a linear function of the product of the magnitude of the signal alongline +V and that along line TD. The output signal from multiplier QAMproduced in response to any signals along lines -+V and TD generatesapplied voltages for phase windings A, B and C which balance the leakageand synchronous reactance, or total IX, voltage drops across eachwinding produced at the speed represented by the signal along line +Vand by the currents then flowing in the windings. By synchronousreactance is meant the apparent reactance resulting from armaturereaction.

Since each output signal from amplifier DAS generates applied voltagesfor the phase windings which not only balance the counter electromotiveforces which would be produced in the windings at no load at the speedat which the rotor is rotating but also the IR voltage drops producedacross the windings by the current then flowing therein and-each outputsignal from multiplier QAM generates applied voltages for the phasewindings which balance the total IX voltage drops produced across thewindings by the current then flowing therein, it is evident from wellknown synchronous motor analysis that the vector sum of voltages foreach winding produces the voltage to be applied to the respectivewinding for each condition of speed and torque.

Direct axis summing amplifier DAS, quadrature axis multiplier QAM, therotor position transducer and the signal or vector summing amplifiers 18through 27 comprise what is hereinafter referred to as transducingapparatus. This apparatus in combination with the hereinbefore mentionedsignal translating apparatus and with the hereinafter disclosedsummation circuit 28 comprise the voltage generating means.

The input signal applied along line TD to both direct axis summingamplifier DAS and quadrature axis multiplier QAM is transmitted fromsummation circuit 28- along line- V through the preamplifier circuitPSN. Preamplifier PSN may also suitably include stability, or responseshaping,,networks to provide a response for the system as desired.

One of the input signals to summation circuit 28 is a desired speedsignal applied along line V from speed dictation apparatus 30. Thissignal is algebraically added to the other input signal, the actualspeed signal, applied along line V from tachometer generator 15, toproduce the output difference signal. Speed dictation apparatus 30 inthe disclosed elevator system may take any one of a number of suitableforms, one such being that disclosed in US. Pat. No. 3,552,524 grantedto Sidney Howard Benjamin and Otto Albert Krauer on Jan. 5, 1971.

The functioning of the various components under operating conditionswill aid in understanding the invention. Assume the elevator car isstopped level with a landing that its doors are open and that the numberof passengers in the car are heavy enough to produce a condition ofbalanced, or no net, load, i.e. the combined weight of the passengersand the car equals the weight of the counterweight. Also assume that thebrake (not shown) is lifted so that the rotor is free to move inresponse to a change in the weight of the passengers in the car or inresponse to torque developed by the motor.

Also, assume that the axes of the magnetomotive forces of the poles ofrotor 14 are each displaced 9O electrical degrees from the physicallocation of the axes of the phase windings A of the stator poles. Underthese conditions the desired speed signal from speed dictation apparatus30 is zero so that no signal is applied to first summation circuit 28along line V Tachometer generator 15 is also applying no signal alonglines -V- and +V to summation circuit 28 and direct axis summingamplifier DAS and quadrature axis multiplier QAM. As a result, there isno difference signal applied by summation circuit 28 to preamplifierPSN. This means that there is no torque required from the motor and sono signal is applied along line TD to direct axis summing amplifier DASand quadrature axis multiplier QAM either.

As a result, no current is applied to any of the Hall effect elementsA1, A2, etc. and they produce no output voltages. Thus, no voltages aretransmitted along lines E,,, E, and E and no voltages are applied tomotor phase windings A, B and C.

Assume now that the number of passengers on the car has increased fromthat which produced the previously assumed condition of balanced load tothat which produces a condition of approximately percent of full ratedload. In actual practice this type of change is a relatively slowhappening one which gradually stretches the hoist ropes causing the carto tend to move down away from the landing. This is counteracted by thelifting of thebrake and the application of power to the motor to restorethe car to within a desired accuracy of the landing. For presentpurposes,

however, the stretch of the ropes will be neglected and it will beassumed that the car is once again stopped at the landing in astabilized condition with its brake lifted.

Suitably in response to the application of this load on the car thecontrol system maintains it at a distance of Because rope stretch isbeing neglected, this one-tenth of an inch is reflected at sheave l3 androtor 14 by a clockwise rotation of approximately 0.32 mechanicaldegrees (as viewed in the drawing). Since the motor has 14 poles, thismechanical rotation is equivalent to 2.24 of electrical rotation.

Simultaneously, speed dictation apparatus 30, which includes the typicalelevator selector mechanism (not shown), produces an electrical signalrepresentative of the one-tenth of an inch the car is below the level ofthe landing or the 0.32 mechanical degrees rotor 14 has rotated. Thissignal is applied along line V to summation circuit 28 where it isalgebraically added to the signal along line -V from tachometergenerator 15. Since under the assumed conditions car is not moving thesignal along line -V is zero. Thus, summation circuit 28 produces anoutput signal along line V which is proportional to the magnitude of thesignal along line V In the disclosed embodiment summation circuit 28 hasa to 1 gain with the result that the signal applied along line V usunder the assumed conditions is 20 times as large as the signal appliedalong line V With the speed dictation apparatus of the forementionedBenjamin and Krauer patent at approximately one-tenth of .an inch from alanding an output signal of approximately 6.35 millivolts is produced.Thus, summation 1 circuit 28 produces an output voltage in response tothis input of approximately 127 millivolts. Preamplifier PSN also has again of 20 to l and this 127 millivolt signal causes the preamplifier toproduce approximately a 2.54 volt signal along line TD and apply it asinputs to direct axis summing amplifier DAS and quadrature axismultiplier QAM.

Since rotor 14 is assumed to be at standstill no signal is applied alongline +V and thus the output of quadrature axis multiplier QAM is zero.Amplifier DAS, however, produces an output current of approximately0.882 milliamps for each volt of input along line TD. Thus the 2.54 voltsignal applied along line TD to direct axis summing amplifier DAS causesan output current of approximately 2.24 milliamps to flow to direct axisHall effect elements A1, B1 and C1 corresponding to phase windings A, Band C, respectively. The result of the application of this current toHall effect elements A1, B1 and Cl combined with the physical rotationof rotor 16 through 2.24 mechanical degrees in the clockwise direction(as viewed in the drawing) is that element A]. produces an outputvoltage of 5.66 millivolts,

' element Bl produces an output voltage of -2.61 millivolts and elementC1 produces an output voltage of -3.05 millivolts.

These voltages are applied to the signal summing amplifier circuitryincluding amplifiers 18 through 27 and result in voltages above groundon lines E E and E; of 5.66 millivolts, 2.61 millivolts and -3.06millivolts, respectively. Upon application of these signal voltages totheir associated pulse generators APG, BPG and CPG the gate controlcircuitry operates to enable the associated inverters A1, B1 and Cl toapply voltages of 5.66 volts, -2.61 volts and 3.05 volts to theirrespective stator phase windings A, B and C. Since each of the statorwindings in the disclosed embodiment has a dc. resistance ofapproximately 0.035 ohms these voltages produce currents in each oftheir respective windings of l6l.7 amperes, 74.6 amperes and 87.1amperes. The currents in the stator phase windings are of oppositepolarity to their applied voltage in accordance with the polaritiesassumed for the disclosed embodiment. These currents provide a resultantmagnetomotive force in each of the stator poles of sufficient magnitudeand the axis of which is at approximately a angle with the axis of themagnetomotive force of each associated rotor pole to provide sufficienttorque to balance the torque applied by the approximate percent fullload to maintain the load at one-tenth of an inch of the landing withrotor 14 at zero angular velocity.

Assume now that the motor has been accelerated to a constant speed inresponse to a desired speed signal equivalent to 127.5 r.p.m. while theload applied to the rotor continues to remain at the previouslymentioned approximate 100 percent full load condition. How theacceleration operation takes place will not be explained for the sake ofconciseness but will be apparent from the following description of theoperation of the servomechanism under the assumed conditions in whichthe effect of speed on the operation of amplifier DAS and multiplier QAMis explained.

To dictate full speed of 127.5 rpm. the selector mechanism of theforegoing Benjamin and Krauer patent applies a voltage of 7.55 voltsalong line V With full load in the car, however, the elevator does notmove at 1,200 f.p.m. or the equivalent of rotor 14 rotating at 127.5r.p.m. because part of the speed dictation signal is employed togenerate the torque required by the load. 1n the disclosed embodimentthis part of the signal amounts to approximately 0.1 percent of therated speed signal. Thus, in response to a desired rated speed signal of7.55 volts at full load rotor 14 rotates at a speed of 99.9 percent ofrated speed and tachometer generator 15 produces a signal not of 7.55volts but of 7.544 volts.

As a result, with the same load in the car a signal of 2.54 volts isagain applied along line TD. As before, this causes amplifier DAS toproduce a current of 2.24 milliamps or 0.882 milliamps for each volt ofsignal along line TD. At the same time a signal of 7.544 volts isapplied to amplifier DAS along line +V which at the scale factor of 15milliamps for each volt of signal along line +V produces an outputcurrent of 113.0 milliamps. Added to the 2.24 milliamps produced inresponse to the signal along line TD, this produces an output currentfrom amplifier DAS of 115.24 milliamps.

At the same time the 2.54 volt signal along line TD and the 7.544 voltsignal along line +V are applied to multiplier QAM and produce an outputcurrent of approximately 44.2 milliamps, multiplier QAM being linearlyscale to produce 2.2 milliamps for each unit of the product of thesignals along lines TD and +V These signals from amplifier DAS andmultiplier QAM are applied to Hall effect elements A1, B1 and C1 and A2,B2 and C2, respectively, and cause sinusoidal voltages to be producedacross lines E E, and E which are out of phase with each other. Each ofthese voltages is also 90 out of phase with its associated quadraturevoltage produced across lines E E and E The maximum magnitude of each ofthe voltages across lines E E and E is 288.6 millivolts. The maximummagnitude of each of the voltages across lines E E and E is 105.5millivolts. The frequency of each of these six voltages is approximately15 c.p.s.

The voltages across these six lines from the rotor position transducerare applied to the signal summing amplifier circuitry in which each pairis vectorially summed to produce sinusoidal voltages along lines E E andE which are 120 out of phase with each other and each of which has amaximum magnitude of approximately 307 millivolts. In addition thevoltages along lines E,,, E and E are each approximately 20 out of phasewith the voltage outputs of the direct axis Hall effect elements A1, B1and C1.

These voltages are transmitted to the signal translating apparatus whichthereupon applies l5 c.p.s. sinusoidal voltages to phase windings A, Band C, which have a maximum magnitude of 307 volts and are in phase withtheir respective associated voltages along lines E E and E Thesevoltages produce currents which generate a resultant magnetomotive forcefor each stator pole the axis of which is at approximately 90 with theaxis of the magnetomotive force of its re spective rotor pole. Thus,substantially all of the current is employed to produce torque. As willbe understood, in the arrangement according to this invention thisphenomenom is true for all magnitudes of applied voltage andconsequently the motor produces substantially maximum attainable torquefor all magnitudes of applied voltage because the out of phase currentsare maintained at a minimum whereby the motor operates at peakefficiency for any load within its rated capacity as well as any loadabove that capacity until magnetic saturation of the stator yoke of themotor is reached.

From the foregoing it will be understood that the disclosedservomechanism includes a polyphase alternating current synchronousmotor and operates in response to a signal signifying a desired speedfor the motor produced by speed dictating apparatus and a signalsignifying the actual speed of the motor produced by speed responsivesignal means. These signals cause a voltage generating means to applyvoltage to said motor to control said motor to deliver torque to main-'tain a load which is continuously applied to the rotor of said motor atzero angular velocity. Moreover, the motor maintains such a load at anyangular position of its rotor. By this is meant that there is noposition of the rotor at which it cannot remain at zero angular velocitywhile a load is applied to it. Thus, when reference is made to anyangular position of the rotor herein it is to be understood that thismeans that each of the infinite positions of the rotor is to beconsidered one at a time until all are considered.

In addition, the voltage generating means is operable in response to thedifference between the desired speed signal and the actual speed signalto apply voltage to said motor to move any load within its ratedcapacity in any desired predetermined manner within its torque producingcapabilities. The voltage generating means includes a first summationcircuit which is responsive to the desired and actual speed signals toproduce a signal signifying the difference between these speeds. It alsoincludes transducing apparatus which operates in response to thisdifference signal and produces signals signifying the individualvoltages to be applied to the stator phase windings of the motor. Thesevoltages cause the stator windings to produce a resultant statormagnetomotive force for each pole of the stator. The axis of each ofthese forces throughout the torque producing range of the motor is atapproximately a 90 angle with the axis of the magnetomotive force of thecorresponding pole of the rotor and the magnitude of each of theseforces is properly related to the magnitude of the magnetomotive forceof the corresponding pole of the rotor to move the load in accordancewith the desired speed signal.

The transducing apparatus of the voltage generating means includes arotor position transducer connected to the rotor of the motor.'Thistransducer operates to produce two voltages for each phase winding ofthe motor. One of these is a signal voltage signifying the magnitude,frequency and phase of the voltage to be applied to the associated phasewinding to balance the counter electromotive force produced by-and theresistance voltage. drop existing across the phase winding for theinstantaneous speed at which the rotor is then rotating and the currentthen flowing in the winding. The other is a signal voltage signifyingthe magnitude,

frequency and phase of the voltage to be applied to the associated phasewinding to balance both the leakage and the synchronous reactancevoltage drop existing across the phase winding for the current thenflowing in the winding. These signal voltages for each phase winding arevectorially summed in signal summing amplifier circuitry, which alsoconstitutes part of the transducing apparatus, to produce signalssignifying the magnitude, frequency and phase of the individual voltagesto be applied to the stator windings in order to insure that the axis ofeach of the resultant magnetomotive forces of the stator is atapproximately a angle with the axis of the corresponding magnetomotiveforce of the rotor. Signal translating apparatus, which forms part ofthe voltage generating means, operates in response to the output signalsof the signal summing amplifier circuitry to apply the individualvoltages to the respective stator phase windings.

The rotor position transducer includes a cylindrical stator yoke ofmagnetic material and a two pole permanent magnet rotor mounted forrotation in the cylindrical stator yoke. This rotor produces asinusoidal flux distribution through the stator yoke. It is mechanicallyconnected to the rotor of the motor for rotation therewith. A pluralityof Hall effect elements, two for each phase winding of the motor, aremounted at intervals around the interior surface of the stator yoke. Thephysical location of a different one of such elements corresponds withthe physical location of a different one of the axes of the individualphase windings of a stator pole of the motor and another such element isin quadrature with each such corresponding element.

The two pole permanent magnet rotor of the rotor position transducer isgeared to the rotor of the motor so that one of the transducer polespasses the Hall effect element in quadrature with that elementcorresponding to one of the phase windings of a stator pole of the motoreach time one of the poles of the rotor of said motor passes thephysical location of the axis of the corresponding stator pole phasewinding.

The transducing apparatus also includes a direct axis summing amplifierand a quadrature axis multiplier. Each of these receives the differencespeed signal and a signal signifying the actual speed of rotation of themotor. The direct axis summing amplifier operates in response to thesesignals to apply an input current to each of the Hall effect elementscorresponding to one of the phase windings of a stator pole of themotor. The

magnitude of this current is the sum of a function of the differencespeed signal and a function of the actual speed signal. The quadratureaxis multiplier operates in response to the difference speed signal andthe actual speed signal to apply an input current to each of thequadrature Hall effect elements whose magnitude is a function of theproduct of the two input signals.

With the foregoing servomechanism it is apparent that an alternatingcurrent polyphase synchronous motor can be started under load from anyangular position of its rotor and can be operated either clockwise orcounterclockwise at any angular speed from zero angular velocity to arated angular velocity. The motor either receives electrical energy froma supply thereof to produce torque continuously to maintain its rotor ata particular angular velocity when the load applied to the rotor tendsto cause it to rotate at a lesser velocity or receives torquecontinuously and transmits electrical energy back to the supply ofelectrical energy to maintain its rotor at a particular angular velocitywhen the load applied to the rotor tends to cause it to rotate at agreater velocity. In addition, starting, acceleration and decelerationare all controllable in any predetermined manner within the torqueproducing capacity of the motor. Moreover, throughout its torqueproducing range the motor operates at peak efficiency since the anglebetween the axis of the resultant magnetomotive force of each statorpole of the motor and the axis of the .magnetomotive force of thecorresponding rotor pole is maintained at approximately 90. Since thetorque produced by the motor is the product of all the resultant statormagnetomotive forces multiplied by the rotor magnetomotive forcesmultiplied by the sine. of

the angle between each pair of forces, maintaining the angle atapproximately 90 minimizes the current required to produce anyparticular torque.

It should also be understood that the disclosed scalar values of directaxis summing amplifier DAS and quadrature axis multiplier QAM areconsidered ideal and not critical. The values disclosed for thedescribed embodiment are chosen to maintain the out of phase currents ata minimum and the axes of the resultant stator magnetomotive-forces atapproximately 90 with the axes of the corresponding rotor magnetomotiveforces. The-effects of reasonable deviations from the ideal, forwhatever reason, in a particular embodiment would be essentiallynullified by the gain of the servomechanism with the result that suchdeviations, at worst,.would only cause some small out of phase currentcomponents.

Modifications in the foregoing apparatus are possible. For example, itis contemplated that cycloconverters may be substituted for the hereindisclosed inverter circuitry. Various other modifications are alsoconsidered'possible without departing from the scope of the invention.Consequently, it is intended that the embodiment specifically describednot be considered exclusive or in any sense limiting.

What is claimed is:

l. A servomechanism including a polyphase alternating currentsynchronous motor which produces torque in accordance with applied loadat any angular position of the motor rotor through its speed range fromzero angular velocity to a rated synchronous velocity, said systemincludingtransducing apparatus operating in response to a signalsignifying the torque it is desired that the motor produceand a signalsignifying the instantaneous speed of the motor to produce at least onepair of signals associated with one of said phase windings the magnitudeof each of the signals of each of .said pairs varying in accordance withthe desired torque and the instantaneous speed of the rotor throughoutits speed range, and a voltage generator operating in response to saidpairs of signals and applying to each phase winding of the motor statoran individual stator voltage to control said motor to produce saiddesired torque, each of said stator voltages being produced in responseto one of said pairs of signals.

2. A servomechanism according to claim 1, wherein said transducingapparatus operates to produce an individual pair of signals for eachphase winding of said motor, and wherein the terminal voltage applied toeach phase winding is produced in response to the pair of signalsindividual to its respective phase winding.

3. A servomechanism according to claim 2, wherein said transducingapparatus includes a summing amplifier and a multiplier, both receivingsaid desired torque signal and said instantaneous speed signal andoperating in response to the magnitudes thereof, the summing amplifierproducing a signal signifying a sum of the magnitudes of said tworeceived signals and the multiplier producing a signal signifying aproduct of the two magnitudes.

4. A servomechanism according to claim 3, wherein one of the signals ofeach pair of signals produced by said transducing apparatus is generatedin response to the output signal of said summing amplifier and the othersignal of each pair is generated in response to the output signal ofsaid multiplier.

5. A servomechanism according to claim 4, wherein said transducingapparatus comprises a rotor position transducer including a cylindricalstator yoke of magnetic material, a two pole'permanent magnet rotormounted for rotation on said yoke and producing a sinusoidal fluxdistribution therethrough,.said two pole rotor being mechanicallyconnected to the rotor of said motor for rotation therewith and aplurality of Hall effect elements, two such elements for each phasewinding of said motor, said elements being mounted at intervals aroundthe interior surface of said yoke so that the physical location of adifferent one of said elements corresponds with the physical location ofthe axis of a different one of the individual phase windings of astattor pole of said motor and another such element is in quadraturewith each such corresponding element.

6. A servomechanism according to claim 5, wherein said two pole rotor ofsaid rotor position transducer is geared to the rotor of said motor sothat one of the poles of said transducer rotor passes the Hall effectelement in quadrature with the element corresponding to one of the phasewindings of a stator pole of said motor each time one of the poles ofthe motor rotor passes the physical location of the axis of thecorresponding stator pole phase winding.

7. A servomechanism according to claim 6, wherein each of saidcorresponding Hall effect elements receives theoutput signal of saidsumming amplifier and generates one of the signals of one of the pair ofsignals, said one signal signifying that component of the terminalvoltage for its associated phase winding which balances both thecounterelectromotive force which would be produced across said phasewinding at no load at the speed at which the rotor is then rotating andthe resistance voltage drop produced across said phase winding by thecurrent it is then conducting.

8. A servomechanism according to claim 7, wherein each of said Halleffect elements in quadrature receives the output-signal of saidmultiplier and generates the other of the signals of one of the pairsofsignals, said other signal signifying that component of the terminalvoltage for its associated phase winding which balances the leakage andsynchronous reactance voltage drop produced across said phase winding bythe current it is then conducting and at the speed at which the rotor isthen rotating.

9. A servomechanism according to claim 8, wherein said transducingapparatus includes signal summing amplifier circuitry for each phasewinding of said motor, each said signal summing amplifier circuitryreceiving the signal produced by the corresponding and quadrature Halleffect elements associated with its respective phase winding andproducing an output signal signifying the vector sum of said signals.

10. A servomechanism according to claim 9, including speed dictationapparatus generating a signal signifying a desired speed for said motorand a speed responsive generator generating a signal signifying theactual speed of said motor, and a summation circuit responsive to saiddesired and actual speed signals producing said desired torque signal.

11. A control system for a polyphase alternating current synchronousmotor operable to control said motor to produce torque inresponse to acontinuously applied load with the rotor of said motor at any angularposition and at any speed from zero angular velocity to a rated runningspeed, said system including speed dictation apparatus generating asignal signifying a desired speed for said motor, a speed responsivegenerator generating' a signal signifying the actual speed'of saidmotor, a summation circuit responsive to said desired and actual speedsignals and producing a desired torque signal, transducing apparatusresponsive to said desired torque signal and said actual speed signaland producing a pair of signals for each of the phase windings of saidmotor, the magnitude of one of the signals of each pair varying inresponse to the sum of the magnitudes of said desired torque signal andsaid actual speed signal, the magnitude of the other of the signals ofeach pair varying in response to the product of the magnitudes of saiddesired torque signal and said actual speed signal, and a voltagegenerator applying to each phase winding of the motor stator anindividual stator voltage to control said motor to produce said desiredtorque in response to the pair of signals associated with the respectivephase winding.

12. A control system according to claim 11, wherein said one signal ofeach pair signifies that component of the terminal voltage applied toits associated phase winding which balances both thecounterelectromotive force which would be produced across said phasewinding at no load at the speed at which the rotor is then rotating andthe resistance voltage drop produced across said phase winding by thecurrent it is then conducting and wherein said other signal of'each pairsignifies that component of the terminal voltage applied to itsassociated phase winding which balances the leakage andsynchronousreactance voltage drop produced across said phase winding by the currentit is then conducting and at the speed at which the rotor is thenrotating.

1. A servomechanism including a polyphase alternating currentsynchronous motor which produces torque in accordance with applied loadat any angular position of the motor rotor through its speed range fromzero angular velocity to a rated synchronous velocity, said systemincluding transducing apparatus operating in response to a signalsignifying the torque it is desired that the motor produce and a signalsignifying the instantaneous speed of the motor to produce at least onepair of signals associated with one of said phase windings, themagnitude of each of the signals of each of said pairs varying inaccordance with the desired torque and the instantaneous speed of therotor throughout its speed range, and a voltage generator operating inresponse to said pairs of signals and applying to each phase winding ofthe motor stator an individual stator voltage to control said motor toproduce said desired torque, each of said stator voltages being producedin response to one of said pairs of signals.
 2. A servomechanismaccording to claim 1, wherein said transducing apparatus operates toproduce an individual pair of signals for each phase winding of saidmotor, and wherein the terminal voltage applied to each phase winding isproduced in response to the pair of signals individual to its respectivephase winding.
 3. A servomechanism according to claim 2, wherein saidtransducing apparatus includes a summing amplifier and a multiplier,both receiving said desired torque signal and said instantaneous speedsignal and operating in response to the magnitudes thereof, the summingamplifier producing a signal signifying a sum of the magnitudes of saidtwo received signals and the multiplier producing a signal signifying aproduct of the two magnitudes.
 4. A servomechanism according to claim 3,wherein one of the signals of each pair of signals produced by saidtransducing apparatus is generated in response to the output signal ofsaid summing amplifier and the other signal of each pair is generated inresponse to the output signal of said multiplier.
 5. A servomechanismaccording to claim 4, wherein said transducing apparatus comprises arotor position transducer including a cylindrical stator yoke ofmagnetic material, a two pole permanent magnet rotor mounted forrotation on said yoke and producing a sinusoidal flux distributiontherethrough, said two pole rotor being mechanically connected to therotor of said motor for rotation therewith and a plurality of Halleffect elements, two such elements for each phase winding of said motor,said elements being mounted at intervals around the interior surface ofsaid yoke so that the physical location of a different one of saidelements corresponds with the physical location of the axis of adifferent one of the individual phase windings of a stator pole of saidmotor and another such element is in quadrature with each suchcorresponding element.
 6. A servomechanism according to claim 5, whereinsaid two pole rotor of said rotor position transducer is geared to therotor of said motor so that one of the poles of said transducEr rotorpasses the Hall effect element in quadrature with the elementcorresponding to one of the phase windings of a stator pole of saidmotor each time one of the poles of the motor rotor passes the physicallocation of the axis of the corresponding stator pole phase winding. 7.A servomechanism according to claim 6, wherein each of saidcorresponding Hall effect elements receives the output signal of saidsumming amplifier and generates one of the signals of one of the pair ofsignals, said one signal signifying that component of the terminalvoltage for its associated phase winding which balances both thecounterelectromotive force which would be produced across said phasewinding at no load at the speed at which the rotor is then rotating andthe resistance voltage drop produced across said phase winding by thecurrent it is then conducting.
 8. A servomechanism according to claim 7,wherein each of said Hall effect elements in quadrature receives theoutput signal of said multiplier and generates the other of the signalsof one of the pairs of signals, said other signal signifying thatcomponent of the terminal voltage for its associated phase winding whichbalances the leakage and synchronous reactance voltage drop producedacross said phase winding by the current it is then conducting and atthe speed at which the rotor is then rotating.
 9. A servomechanismaccording to claim 8, wherein said transducing apparatus includes signalsumming amplifier circuitry for each phase winding of said motor, eachsaid signal summing amplifier circuitry receiving the signal produced bythe corresponding and quadrature Hall effect elements associated withits respective phase winding and producing an output signal signifyingthe vector sum of said signals.
 10. A servomechanism according to claim9, including speed dictation apparatus generating a signal signifying adesired speed for said motor and a speed responsive generator generatinga signal signifying the actual speed of said motor, and a summationcircuit responsive to said desired and actual speed signals producingsaid desired torque signal.
 11. A control system for a polyphasealternating current synchronous motor operable to control said motor toproduce torque in response to a continuously applied load with the rotorof said motor at any angular position and at any speed from zero angularvelocity to a rated running speed, said system including speed dictationapparatus generating a signal signifying a desired speed for said motor,a speed responsive generator generating a signal signifying the actualspeed of said motor, a summation circuit responsive to said desired andactual speed signals and producing a desired torque signal, transducingapparatus responsive to said desired torque signal and said actual speedsignal and producing a pair of signals for each of the phase windings ofsaid motor, the magnitude of one of the signals of each pair varying inresponse to the sum of the magnitudes of said desired torque signal andsaid actual speed signal, the magnitude of the other of the signals ofeach pair varying in response to the product of the magnitudes of saiddesired torque signal and said actual speed signal, and a voltagegenerator applying to each phase winding of the motor stator anindividual stator voltage to control said motor to produce said desiredtorque in response to the pair of signals associated with the respectivephase winding.
 12. A control system according to claim 11, wherein saidone signal of each pair signifies that component of the terminal voltageapplied to its associated phase winding which balances both thecounterelectromotive force which would be produced across said phasewinding at no load at the speed at which the rotor is then rotating andthe resistance voltage drop produced across said phase winding by thecurrent it is then conducting and wherein said other signal of each pairsignifies that component of the terminal voltage applied to itsassociated phase windIng which balances the leakage and synchronousreactance voltage drop produced across said phase winding by the currentit is then conducting and at the speed at which the rotor is thenrotating.